1. Field of the Invention
The present invention relates to a collet which is used to hold a tool, and which is inserted into a tool holder mounted to a main spindle of, for example, a machine tool.
2. Description of the Related Art
In tool machines such as lathes, drilling machines, or milling machines, collets have been used as a part of holders for holding tools such as drills or end mills. This type of collet generally comprises a collet body, into which the shank of the tool is inserted, and a slot formed in the collet body.
It is necessary to cool these tools continuously in order to suppress heat generated at the time of processing (cutting) works. The tools are sometimes lubricated in order to obtain better workability. As a general method for such cooling and lubrication, a water-soluble coolant or a cutting fluid (cooling fluid) such as oil is supplied to the tool. As an example of the method for supplying the cutting fluid to a tool, a tool with a through hole extending in its lengthwise direction is used and the tool is cooled by causing the cutting fluid to flow through the through hole. This method is intended to supply the cutting fluid to the through hole in the tool efficiently by providing a weir member at a specified position of the slot in order to prevent the cutting fluid from flowing out from the slot formed in the collet body.
When a tool is used which has no through hole as described above, there is a general method for cooling the tool by supplying the cutting fluid between the collet and the tool held by the collet by utilizing the slot formed in the collet body.
In the method of cooling the tool by supplying the cutting fluid to the tool by utilizing the slot formed in the collet body, if the tool held by the collet has a small diameter relative to the outside diameter of the collet body, a cross-sectional area of the slot in its radial direction becomes large and, therefore, the flow velocity of the cutting fluid is reduced accordingly. As a result, there is a fear that the cutting fluid may become easily dispersed and it may become difficult to supply the cutting fluid to the cutting edge of the tool in a concentrated manner. Particularly, there is a fear that even if the cutting fluid is supplied at high pressure, the cutting fluid may be dispersed due to centrifugal force at the time of high-speed rotation before it reaches the cutting edge of the tool.
The present invention is aimed at improving the conventional collets as described above. It is an object of this invention to provide a collet which can efficiently supply a cooling fluid such as a cutting fluid to the tool by adjusting the flow velocity of the fluid according to the diameter of the tool held by the collet, thereby enabling satisfactory cooling.
In order to achieve the above-described object, the present invention provides collet for holding a tool by inserting the shank of the tool into a center hole of the collet mounted in a tool holder for supplying a fluid to the tool, and the collet comprises: a collet body for inserting the shank of the tool therein; a slot formed at least from the tool insertion side of the collet body; and a weir member inserted into the slot. The weir member extends from a position recessed from the inner surface of the collet body in a direction closer to the outer surface of the collet body, thereby forming a gap for the fluid to flow therethrough between the weir member and the inner surface of the collet.
Concerning the collet having the above-described structure, the end face of the weir member inserted into the slot on the side facing the inner surface of the collet body is located at a position recessed from the inner surface of the collet body in a direction closer to the outer surface of the collet body, thereby forming a gap between the weir member and the inner surface of the collet body, through which the fluid flows. Accordingly, by changing the cross-sectional area of the gap arbitrarily by adjusting the position of the end face of the weir member on the side facing the inner surface of the collet body according to the diameter of the tool held by the collet, it is possible to adjust the flow velocity of the cooling fluid such as the cutting fluid.
The cross-sectional area of the gap in the radial direction of the collet body can be determined by adjusting the length of the weir member. In other words, the cross-sectional area of the gap can be relatively decreased by extending the length of the weir member, while the cross-sectional area of the gap can be relatively increased by shortening the length of the weir member. Concerning the collet of this invention, a weir member insertion hole can be formed in the slot in the radial direction of the collet body, and the weir member can be inserted into the weir member insertion hole.
Moreover, at one end of the weir member on the side facing the inner surface of the collet body, an inclined plane can be formed which is inclined from the outer surface of the collet body to the inner surface thereof toward the tool insertion side. This inclined plane guides the cooling fluid to the cutting edge of the tool, thereby enabling more efficient cooling of the tool.
Furthermore, regarding the collet of this invention, a weir member insertion hole can be formed in the slot, which is inclined from the outer surface of the collet body to the inner surface thereof toward the tool insertion side, and the weir member can be inserted into the weir member insertion hole. This structure allows the cooling fluid to be guided to the cutting edge of the tool, thereby enabling more efficient cooling of the tool.
The weir member can be located in the vicinity of the tool insertion side. By so locating the weir member, the cooling fluid can be guided to the cutting edge of the tool more easily, thereby enabling the cooling of the tool with further efficiency.
Moreover, the weir member can be made of an elastic element.
The slot can be formed to have different widths at a position closer to the base-end side than to the weir member and at a position closer to the top-end side than to the weir member. This structure makes it possible to adjust the flow velocity of the cooling fluid more effectively.
The collet of this invention may be a straight collet or a tapered collet.
The weir member can be located in a nut mounting part of the collet body of the tapered collet. The weir member can also be located in a tapered part of the collet body.